1. Field of the Invention
The present invention relates to a sling to be fastened around an object which is to be raised or moved by a crane or hoist, and more particularly to a belt which can be used to produce such sling.
2. Description of the Prior Art
Generally speaking, wire ropes are widely used as a sling so as to raise and move an article. However, the wire ropes lack flexibility and weigh so much as to make their fastening operations around the article difficult. In order to eliminate such difficulty, a rope or belt made of fibers has recently been used as a sling. The requirements for the fibrous sling rope or belt of that kind are that it has a low elongation, close to that of the wire rope and that it has excellent anti-abrasiveness properties and strength. If a sling has a relatively large elongation, it may fail to securely hold an article during the lifting operation so that the article will fall from the sling. This may result in a dangerous accident, which has to be obviated from safety consideration. From this consideration, therefore, polyester synthetic fibers, which are known to have a relatively small elongation, can be said suitable as the material for a fibrous sling belt. The polyester synthetic fibers are, however, inferior in anti-abrasiveness to polyamide synthetic fibers. With this fact in mind, there has been developed a sling belt of wadded double fabric which can suitably satisfy the above conditions by using as the core material the filament yarns of polyester synthetic fibers having a smaller elongation and as the sheath material filament yarns of polyamide synthetic fibers having excellent anti-abrasiveness.
The invention, which was filed for Japanese Utility Model Registration on Dec. 18, 1973 by the Applicant of the present Patent Application and which can be located in Japanese Utility Model Publication No. 53-14777 published on Apr. 19, 1978, is also directed to a sling belt having the structure thus far described. The sling belt disclosed is composed of: a sheath which is prepared by plainly weaving the warp yarns and the weft yarn of polyamide synthetic fibers such as nylon; a core which is arranged in the sheath and which is prepared by plainly weaving this warp yarns of polyester synthetic fibers such as Tetrone (Registered Trade Name) with the weft yarn leading to and from that of the sheath such that the interlacing points of the core are made fewer than those of the sheath; and binder warp yarns which are woven at a suitable spacing to intersect alternately thereby to bind together the both sides of the sheath. Thus, the sling belt has the weave of wadded double fabric, in which the sheath and core are dyed in different colors. This belt is remarkably excellent in endurability and safety in comparison with the belt of the prior art.
As is well known in the relevant art, in the case of normal use of a belt sling, it is only one side of the sheath that is brought into direct contact with an object to be lifted. This face side, to contact with the object, is subject to more abrasion than the back side. Since the sling belt uses the abrasion of its sheath as a measure of its disposal, its life would be uselessly shortened if the face side of higher abrasiveness were made to have the same thickness as that of the back side of lower abrasiveness. The aforementioned sling belt disclosed in the Japanese Utility Model Publication has the face and back sides of the same thickness and the resultant drawback.